JP2009218283A - Memory element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a novel nonvolatile memory element which consists of only an anode layer, a cathode layer and a switching layer, enables the switching layer to be manufactured through simple high-yield processes, is rewritable and operates at high speed. <P>SOLUTION: The single switching layer 4 is formed between the anode layer 3 and cathode layer 5, the anode layer 3 and switch layer 4 are joined together directly, and the cathode layer 5 and the switching layer 4 are joined together directly. The switching layer 4 is formed of an organic high polymer having an oxidation-reduction active region. The oxidation-reduction active region is oxoammonium cation salt, N-oxyl anion salt, phenolate anion salt, or aminium cation salt. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a switching element that switches on and off according to an applied voltage and maintains the state, and more particularly to a nonvolatile and rewritable memory element.

  Conventionally, a memory element using a silicon substrate has been widely used. However, a complicated and expensive manufacturing process such as photolithography is required for manufacturing the memory element, so that the memory element as a final product becomes very expensive. was there. Further, in the case of a volatile memory element, DRAM (dynamic random access memory) has a high manufacturing cost, and flash memory and HDD (hard disk drive) have a problem that writing speed and reading speed are slow.

  As an alternative to such a memory element, various rewritable and non-volatile memory elements capable of high-speed operation have been studied. One example is a memory element using an organic material.

  As a memory element using an organic material, an element using an organic low-molecular material as a switching layer is the mainstream, and pentacene (Non-Patent Document 1) and tris (8-hydroxyquinolinato) aluminum (Non-Patent Document 2) are used. An element using such an organic semiconductor has been proposed as a WORM (write once read many) type memory element.

  However, a memory element using such an organic low-molecular material as a switching layer has a problem that a film formation process with a low yield using a vacuum deposition apparatus such as an electron beam method or a sputtering method is essential.

For this problem, a switching layer made of an electrically insulating radical polymer is provided between the anode layer and the cathode layer, and a hole transport layer, a switching layer and a cathode layer are provided between the switching layer and the anode layer. A memory element having an electron injecting and transporting layer between them is disclosed (Patent Document 1). In this memory element, a switching layer, a hole injecting and transporting layer, and an electron injecting and transporting layer can be laminated by a wet method, so that the uniformity of the film quality of each layer can be maintained, and the process is simple and has a high yield. A memory device can be manufactured.
D. Tondelier, K.M. Lmimuni, D.M. Vouilleume, C.I. Ferry, G.M. Haas, Appl. Phys. Lett. 2004, 85, 5762. A. K. Mahapatro, R.A. Agrawal, S.M. Ghosh, J .; Appl. Phys. 2004, 96, 3583. International Publication WO / 2006/049261 Pamphlet

  However, since this memory device has a multilayer structure including a switching layer, a hole injecting and transporting layer, and an electron injecting and transporting layer in addition to the anode layer and the cathode layer, there is a problem that the number of steps required for manufacturing increases. .

  Therefore, the present invention comprises a novel nonvolatile memory element consisting of only an anode layer, a cathode layer, and a switching layer, and capable of producing the switching layer in a simple and high-yield process by a wet method, being rewritable and capable of high-speed operation, And it aims at providing the novel compound which comprises the switching layer.

  The memory element of the present invention comprises a single-layer switching layer between an anode layer and a cathode layer, the anode layer and the switching layer are directly bonded, and the cathode layer and the switching layer are directly bonded. The switching layer is made of an organic polymer having a redox active site.

  The redox active site is an oxoammonium cation salt.

  The redox active site is an N-oxyl anion salt.

  The redox active site is a phenolate anion salt.

  The redox active site is an aminium cation salt.

The compounds of the present invention
It is represented by any one of the following structural formulas (a) to (i) (X ⁻ and A ⁺ are counter ions).

  According to the memory element of the present invention, it is possible to provide a novel nonvolatile memory element which can be manufactured by a wet process in a simple and high yield process, and can be rewritten and operated at high speed.

  According to the compound of the present invention, a novel compound constituting the switching layer of the memory element of the present invention is provided.

  Hereinafter, an embodiment of a memory device of the present invention will be described in detail with reference to the accompanying drawings.

  In FIG. 1 schematically showing a memory element of the present invention, reference numeral 1 denotes a memory element having a laminated structure in which an anode layer 3, a switching layer 4 and a cathode layer 5 are laminated on a substrate 2 in this order. Yes. The switching layer 4 is a single layer, and the anode layer 3 and the switching layer 4, the cathode layer 5 and the switching layer 4 are directly bonded to each other, and the anode layer 3, the switching layer 4, and the cathode layer 5 are It has a film thickness of 1000 nm.

  The material of the substrate 2 is not limited to a specific material, and a glass substrate, a quartz substrate, or the like can be used as the substrate 2. The anode layer 3 is made of a conductive material and is formed on the substrate 2 by a known method. The cathode layer 5 is also made of a conductive material and is formed on the switching layer 4 by a known method.

  The switching layer 4 is made of an organic polymer, and this organic polymer has a redox active site. Note that the oxidation-reduction active site refers to those that are easily oxidized or reduced by application of voltage and become neutral radicals by oxidation or reduction by application of voltage. This redox active site can be rapidly and reversibly redox under low voltage application, and can inject and / or transport holes and / or electrons in the redox behavior with the corresponding neutral radical. Are preferred.

In addition, the electrical conductivity of the organic polymer constituting the switching layer 4 is an approximately intermediate value between the insulator (less than 10 ⁻⁸ S / cm) and the semiconductor (10 ⁻⁸ S / cm to 10 ⁻⁵ S / cm). 10 ⁻⁸ S / cm to 10 ⁻⁷ S / cm. By having this value, it is possible to easily and accurately determine the on / off state of the memory element. Also, this electrical conductivity value is convenient for maintaining the charged state over a long period of time.

  Examples of the organic polymer having such a redox active site and electrical conductivity include, for example, any one of oxoammonium cation salt, N-oxyl anion salt, phenolate anion salt, and aminium cation salt in the structure. Organic polymers possessed by By forming the switching layer 4 using these organic polymers, the switching layer 4 forms a salt paired with an oxoammonium cation and a salt paired with an N-oxyl anion. Or a counter ion that forms a salt by pairing with a phenolate anion, or a counter ion that forms a salt by pairing with an aminium cation. Therefore, the operation of the memory element is stabilized.

  Among these, an oxoammonium salt polymer that is an organic polymer having an oxoammonium cation salt in the side chain is particularly preferably used. This is because the oxoammonium cation has a high electron transport ability by being converted into a nitroxide radical by one-electron reduction, as shown in Chemical Formula 2.

In addition, the redox reaction between the oxoammonium cation and the nitroxide radical is rapid and extremely chemically and electrochemically stable. Furthermore, the oxoammonium salt polymer and the corresponding nitroxide radical polymer also have a thermal stability that enables stable handling up to 250 ° C. in the atmosphere. The electrical conductivity of the oxoammonium salt polymer is 10 ⁻⁸ S / cm.

  As a method for synthesizing an oxoammonium salt polymer, for example, 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) is derived into an oxoammonium salt by chemical oxidation or electrochemical oxidation. An example of the synthesis method is shown in Chemical Formula 3.

Here, X ⁻ represents a counter ion, and X ⁻ represents a halogen ion, BF ₄ ⁻ , PF ₆ ⁻ , COO ⁻ , ClO ₄ ⁻ , SO ₃ ⁻ , which has a one-to-one correspondence with the oxoammonium cation. In addition to such monovalent ones, divalent ones such as SO ₄ ²⁻ corresponding two-to-one are also included.

  The oxoammonium salt polymer is not limited to the above, and can be synthesized by various routes. For example, it can also be obtained by chemically oxidizing the hydroxyl group of N-hydroxy-2,2,6,6-tetramethylpiperidine.

  In addition, a reactive group is introduced into TEMPO, which is a precursor of oxoammonium cation salt, and the monomer is covalently coupled, and this monomer is homopolymerized or copolymerized with another monomer and then oxidized to give oxoammonium cation. It can also be induced into salt. Alternatively, a reactive group may be introduced into the oxoammonium cation salt and coupled to the monomer by a covalent bond, and this monomer may be homopolymerized or copolymerized with another monomer. Alternatively, the nitroxide derivative monomer may be derived into an oxoammonium cation salt monomer by chemical oxidation or electrochemical oxidation, which may be homopolymerized or copolymerized with other monomers.

  Furthermore, in addition to the above oxoammonium salt polymer, a dispersion prepared by blending an oxoammonium cation salt in another organic polymer can also be used as the organic polymer constituting the switching layer 4.

  As the organic polymer constituting the switching layer 4, a phenolate anion salt polymer which is an organic polymer having a phenolate anion salt in the side chain is also preferably used. An example of the synthesis method is shown in Chemical Formula 4.

Here, A ⁺ is a counter ion, and A ⁺ includes alkali metal ions, alkaline earth metal ions, transition metal ions, organic ammonium, and the like.

  The phenolate anion salt polymer is not limited to the above, and can be synthesized by various routes. For example, it can also be obtained by chemically reducing the hydroxyl group of the phenol derivative.

  It is also possible to introduce a reactive group into a phenol derivative and couple it covalently with a monomer, and then reduce this monomer to a phenolate anion salt by homopolymerization or copolymerization with another monomer and then reduction. . Alternatively, a reactive group may be introduced into the phenolate anion salt, and the monomer may be covalently coupled, and this monomer may be homopolymerized or copolymerized with another monomer. Alternatively, the phenol derivative monomer may be derived into a phenolate anion salt monomer by chemical reduction or electrochemical reduction, and this may be homopolymerized or copolymerized with other monomers.

  Furthermore, in addition to the above-described phenolate anion salt polymer, a dispersion prepared by blending a phenolate anion salt into another organic polymer can also be used as the organic polymer constituting the switching layer 4.

An example of an oxoammonium cation salt polymer and a phenolate anion salt polymer that can be used as the organic polymer constituting the switching layer 4 is shown in Chemical Formula 5. A compound represented by any one of these structural formulas (a) to (i) (X ⁻ and A ⁺ are counterions) is a compound of the present invention.

Here, (a) is poly (2,2,6,6-tetramethylpiperidine-1-oxoammonium-4-vinyl ether), and (b) is poly (4-methacryloyloxy-2,2,6). , 6-tetramethylpiperidine-1-oxoammonium), (c) is poly (4-acryloyloxy-2,2,6,6-tetramethylpiperidine-1-oxoammonium), (d) is poly (4 -Nt-butyl-N-oxoammonium styrene), (e) is poly (4-acryloylamino-2,2,6,6-tetramethylpiperidine-1-oxoammonium), (f) is poly (4-Methacryloylamino-2,2,6,6-tetramethylpiperidine-1-oxoammonium), (g) is a poly (4- (2,6-di-t-butyl-α- (3,5 -G-t -Butyl-4-oxo-2,5-cyclohexadiene-1-ylidene) -p-galvinolate), (h) is poly (2- (4,4,5,5-tetramethylimidazoline-1-oxoammonium) ) Styrene) and (i) are poly (2- (4,4,5,5-tetramethylimidazoline-1-aminoxy) styrene), X ⁻ and A ⁺ are the same as in Chemical Formula 3 and Chemical Formula 4. Counter ion.

  In addition, in order to use these organic polymers for the switching layer 4 and to make the memory element function, 10% or more of the monomer needs to be in the state of a cation salt or an anion salt. It is desirable that 100% is in the state of a cation salt or an anion salt.

  Further, by using a high molecular weight organic polymer, the switching layer 4 can be easily formed by a wet method. The molecular weight is preferably several thousand or more, and preferably 10,000 to several hundred thousand. The wet method is a known technique for forming a thin film of an organic polymer, and generally known is a spin coating method, a printing method such as inkjet, a Langmuir-Blodgett method, a self-organization method, or the like. ing. In addition, according to this wet method, the film quality uniformity and amorphous stability of the switching layer 4 and the stability of the higher order structural order are maintained, the yield is high, suitable for mass production, and low-cost manufacturing. It becomes possible.

  Next, the operation will be described.

  When a voltage is applied between the anode layer 3 and the cathode layer 5, the switching layer 4 changes from the low resistance state to the high resistance state. That is, when the voltage applied between the anode layer 3 and the cathode layer 5 is lower than the threshold value, it is in a high resistance state, and when the voltage exceeds the threshold value, it changes to a low resistance state, and the voltage becomes lower than the threshold value again. The low resistance state is maintained. In addition, this threshold value used as a drive voltage can be reduced by making the switching layer 4 thin.

  As described above, the memory element 1 of this embodiment includes the single-layer switching layer 3 between the anode layer 2 and the cathode layer 4, and the anode layer 2 and the switching layer 3 are directly joined to each other. The layer 4 and the switching layer 3 are directly joined together, and the switching layer 3 is made of an organic polymer having a redox active site, and the switching layer 3 can be manufactured by a wet process in a simple and high yield process. A novel nonvolatile memory element that can be rewritten and can operate at high speed can be provided.

  In addition, this invention is not limited to the said Example, A various deformation | transformation implementation is possible.

  The following specific examples further illustrate the present invention.

<Preparation of Memory Element 1>
A substrate (25 × 25 × 1 mm, manufactured by Asahi Glass Co., Ltd.) on which an ITO layer (150 nm) was previously formed on a glass substrate was placed on a spin coater. A solution of poly (2,2,6,6-tetramethylpiperidine-1-oxoammonium-4-vinylether) in acetonitrile on the substrate is 10 seconds at a rotation speed of 1000 rotations / second, followed by 60 rotations at 6000 rotations / second. After spin-coating for 2 seconds, it was dried at 80 ° C. for 2 hours under vacuum to produce a poly (2,2,6,6-tetramethylpiperidine-1-oxoammonium-4-vinylether) thin film 100 nm on the substrate. The substrate on which the ITO / poly (2,2,6,6-tetramethylpiperidine-1-oxoammonium-4-vinyl ether) structure was formed as described above was placed on the substrate holder in the chamber of the vacuum evaporator. A filament wound with Al was attached to the electrode in the chamber. Next, the inside of the chamber was decompressed, and aluminum serving as a cathode was deposited on a 150 nm-thickness substrate in a vacuum degree of 1 to 3 × 10 ⁻⁵ Pa in a deposition rate of ⁵ to 7 liters / second. After the deposition was completed, the inside of the chamber was returned to atmospheric pressure, and the substrate was taken out. As described above, the structure of ITO (150 nm) / poly (2,2,6,6-tetramethylpiperidine-1-oxoammonium-4-vinyl ether) (100 nm) / Al (150 nm) is formed on the glass substrate. A memory element 1 having the same was manufactured.

<Current-voltage characteristics>
When a voltage is applied and swept between the anode layer and the cathode layer in the memory element 1 manufactured as described above, the electrical conductivity changes rapidly at a predetermined threshold voltage. Specifically, when a positive bias is applied after sweeping the applied voltage from 0 V to a negative bias, the current value rapidly increases (2 to 3 digits) at the threshold voltage. That is, the threshold voltage changes from a high resistance state to a low resistance state, and this low resistance state is permanently maintained until a further negative bias voltage is applied. Here, the positive bias is a potential state in which the anode layer is at a high potential with respect to the cathode layer, and the reverse bias is a potential state in which the cathode layer is at a high potential with respect to the anode layer.

  Further, the memory element 1 of the present embodiment exhibits switching characteristics. Here, the switching characteristic means that the applied voltage is swept to the negative bias in the element in the low resistance state (on state), and then the applied voltage is swept to the positive bias again after the high resistance state (off state). In this case, the threshold voltage is a characteristic indicating a change from a high resistance state to a low resistance state.

FIG. 2 shows the results of current-voltage measurement performed by 0.1 V each with the voltage applied between the electrode layers of the manufactured memory element 1 set in the range of −5 to 5 V. The current value was 25 mA at a negative bias applied voltage of −1.4 V, but the current value gradually decreased and changed to a high resistance state with a threshold value of around −1.5 V. In the vicinity of the positive bias applied voltage of 2V, the current value was in a high resistance state of 10 ⁻⁴ A. However, at a positive bias voltage equal to or higher than the threshold (2-2.5 V), the current values were 10 ⁻² A and 10 ^2. It rose and changed to a low resistance state. Moreover, the same low resistance state was maintained by applying more voltage. Next, when a negative bias voltage was applied again, the low resistance state was maintained up to the same threshold voltage, but it changed to the high resistance state again when a voltage higher than the threshold was applied. When a further positive bias voltage was applied, the voltage changed to the low resistance state again by applying a voltage higher than the threshold voltage as in the first voltage sweep. From this, it can be said that the memory element 1 is a rewritable memory element that can be repeatedly switched between on and off states by adjusting the applied voltage.

Further, the memory element 1 exhibited a good state holding force as shown in FIG. Here, a negative bias voltage equal to or higher than a threshold (−1.5 V) set as an erasing voltage is applied between the electrodes to set the memory element state as a high resistance state, that is, an off state, and set as a reading voltage. A permanent high resistance state was evaluated by repeatedly applying a pulse voltage between the electrodes with a positive bias voltage of a threshold value (2 V) or less. Subsequently, by applying a pulse voltage between the electrodes with a positive bias voltage equal to or higher than the threshold (2 V) set as the write voltage, the memory element is set in the low resistance state, that is, in the on state, and set as the read voltage as described above. A permanent low resistance state was evaluated by repeatedly applying a pulse voltage to the positive bias voltage between the electrodes. The read voltage of the memory element 1 was set to 1V, the erase voltage was set to -5V, and the write voltage was set to 5V. Persistent low resistance state and high resistance state as shown in FIG. 3 is turned on / off ratio were stably operate several tens of thousand cycles or more while maintaining 10 ² orders of magnitude.

It is a schematic diagram which shows one Example of the memory element of this invention. 3 is a graph showing measurement results of current-voltage characteristics of the memory element fabricated in Example 1. 6 is a graph showing the evaluation results of the state retention force of the memory element fabricated in Example 1.

Explanation of symbols

3 Anode layer 4 Switching layer 5 Cathode layer

Claims (6)

A single layer switching layer is provided between the anode layer and the cathode layer, the anode layer and the switching layer are directly bonded, the cathode layer and the switching layer are directly bonded, and the switching layer is redox-active. A memory element comprising an organic polymer having a portion. The memory element according to claim 1, wherein the redox active site is an oxoammonium cation salt. The memory device according to claim 1, wherein the redox active site is an N-oxyl anion salt. The memory device according to claim 1, wherein the redox active site is a phenolate anion salt. The memory element according to claim 1, wherein the redox active site is an aminium cation salt. A compound represented by any of the following structural formulas (a) to (i) (X ⁻ and A ⁺ are counterions).

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